Papers by Keyword: Refrigeration

Abstract: It is feasible to obtain low temperature that can liquefy the natural gas using supersonic separator in a liquefaction process. This paper represented a design method of the supersonic separator used in natural gas liquefaction plant, including the design of the Laval nozzle, the design of the rectifier straight segment and the design of the diffuser segment. The size of each part and the appropriate shape can be gotten by the theoretical calculation. The design results of an experiment liquefaction device using supersonic separator is given. The work is helpful for the natural gas transportation in remote and low production gas field.

Abstract: Desalination of seawater has played an important role in many arid regions in the world. There are many methods for desalination of seawater, such as MED, MSF, RO, ED, TVC, and MVC, etc. Different methods have different advantages and disadvantages. In the present work, a new method for desalination of seawater with steam-ejector refrigeration plant was introduced. The main purpose of the new method is a hybrid plant of TVC and steam-ejector refrigeration. In the hybrid circle, no other energy was need. When the steam-ejector refrigeration plant is working, the seawater as cooling water is introduced into evaporator of TVC and evaporates. The vapor getting in TVC is extracted by a second steam-ejector, together with the active steam, is used as source of heat for desalination. The main advantage of this hybrid plant is that part of the heat energy of cooling water in refrigeration is reused. Comparing with other distillation method desalination of seawater, the energy consumption is much less. Especially on marine usage, the advantage is clear.

Abstract: Vapour compression cycles are commonly used in household refrigerators and also in many commercial and industrial refrigeration systems. R-134a is a working fluid widespread in this kind of systems. A chlorine free refrigerant such as R-134a has a disadvantage in the sense of its relatively high Global Warming Potential (GWP), although the specific Ozone Depletion Potential (ODP) is null. International concern over the relatively high global warming potential of R-134a, and other refrigerants belonging to the same family, will lead in the near future to the stop of their production and use. For this reason, the interest in finding of an environmental more benign substitute for this refrigerant is growing. In the meantime, the alternatives for R-134a should be as thermodynamically attractive as this chemical. In this study it is theoretically assessed the opportunity of using R-600a (isobutane) in the future environment friendly vapour compression refrigeration systems. Choosing of isobutane is explained by the fact that it is a naturally occurring refrigerant. During the thermodynamic analysis, R-134a and R-600a are evaluated for a range of evaporating temperatures starting with 25°C and finishing with 0°C. There are considered three levels of the condensing temperature: 30°C, 40°C, 50°C. For these two refrigerants are compared results regarding saturated vapour pressure, Coefficient of Performance, volumetric cooling capacity, compressor discharge temperature, refrigerant mass flow rate. Also, in the scope of future improvement of systems adopting R-600a as a refrigerant, it is performed an exergy analysis, which is able to reveal the hierarchy of inefficiencies in the system. The results obtained indicate that adopting of R-600a instead of R-134a in vapour compression refrigeration systems is a decision motivated not only by environment reasons, but also by thermodynamic arguments. Values for the Coefficient of Performance when using R-600a are slightly lower than when in use is R-134a, but isobutane offers better environmental requirements like zero Ozone Depletion Potential and very low Global Warming Potential. Exergy analysis developed for R-600a as a working fluid revealed that the most inefficient is the compressor. Better exergy efficiency can be obtained for higher values of the evaporating temperature.

Abstract: Comparing with the common jet refrigeration system, a central air conditioner combined with solar ejector refrigeration system was proposed. The system characteristic was presented. It can improve the coefficient of the single solar system and solve operation problem for day-and-night, and can reduce the energy consumption of central air conditioner. A reasonable ejector to match with the central air conditioning is a main component in the system. The ejector in the solar refrigeration system is preliminary analyzed by the pneumatic function method. It will provide the important reference to improving the conditioner performance and system efficiency on air conditioning energy saving.

Abstract: A new model of the refrigerator with refrigeration and constant temperature and hot water has been trial-produced. The new refrigerator can not only keep refrigerated food quality, but also be used for heating or keeping food temperature constant, and supply hot water for us. The subsystems of condenser have been analyzed and designed including air-cooled method and water-cooled method. According to the theoretical calculation, the temperature in constant temperature box can keep about 50°C and 18.46 Kg hot water can be provided per hour.

Abstract: The supermarket refrigeration system typically has a distributed control structure, which simple and flexible, however, neglects interactions between its subsystems. Practice shows that these interactions lead to a synchronous operation of the display cases. It causes excessive wear on the compressors and increased energy consumption. The paper focuses on the synchronization analysis and de-synchronization control. The supermarket refrigeration system is modeled as a piecewise-affine switched system. The system behavior is decomposed such that synchronization analysis can be completed by using the Poincare map. A new de-synchronization scheme is proposed, which includes two steps: the synchronization monitoring and the de-synchronization control. Thus, the early warning of the synchronization can be given and then the de-synchronization controller can be activated. The scheme achieves better control performance and can deal with the large scale refrigeration system with different system parameters in the display cases.

Abstract: A miniature vapor-compression refrigeration system for cooling high power CPUs has been developed and tested. The refrigeration system is so small that it can be embedded into the computer case. The refrigerant used in the system is R-134a. The system consists of a miniature rotary DC compressor, a micro-channel condenser, a specially designed cold plate, a short tube restrictor, and related controlling electronics. The compressor is powered directly by the 12V DC power supply of the computer. The cold plate contacts the CPU surface directly and carries away the heat dissipation by conductivity. In a series of tests to cool an Intel Core i7-990X CPU that has 12 cores inside with the refrigeration system, the CPU core temperature can be kept at 23°C in default frequency 3.5GHz and 100% of workload. When the CPU is overclocked to 4.8GHz, the core temperature can be maintained at 59°C. Even when overclocked to 5.0GHz, the core temperature does not exceed 78°C. The test results validate the ability and potential of using vapor-compression refrigeration technology in high heat flux CPU cooling.

Abstract: Dynamic models of the heating, ventilation and air-conditioning (HVAC) systems in a temperature controlled room are very useful for controller design, commissioning, and fault detection and diagnosis. A transient model is a set of time differential equations in mass, energy and momentum balances. These transient equations contain parameter values for validation. The parameter such as thermal capacitances of the room chamber, heat transfer coefficient of room panel, heat transfer coefficient of evaporator are difficult to determine because they are related to unsteady condition and have to be considered to account for room energy storage. Many researchers have been studied the transient model for HVAC system by setting an assumption that there parameters are already known. None of them has been investigated into the parameter identification. This research work focused into the parameter identification technique to determine the thermal capacitances of the room chamber, heat transfer coefficient of room panel, and heat transfer coefficient of evaporator. The transient model of a refrigeration unit for an air-conditioned room was analyzed. Block diagram technique along with computer simulation technique were applied for the task. Experimental tests were setup to validate this model.

Abstract: The SPI was applied in food industry widely, but the component which could affect the functionalities and it may change during storage. The effect of store temperature, time, RH and package material on SPI oil absorption were studied, when SPI was packaged in 100% N2 and Al, 80%N2:20%CO2 and Al, 60%N2:40% CO2 and Al, vacuum and Al, white paper/plastic/LDPE, and PE and then stored for 5 months in the conditions of RH55%，4°C. It was shown that the 7S/11S of SPI in all packages not change significantly. But it was observed by SDS-PAGE that the subunit of SPI disaggregated and molecules aggregated. Focus on the sulfhydryln group and disulfide bond; it was found that the content of sulfydryl decreases while disulfide bond increased sharply especially in the later three months.

Abstract: A vortex tube offers an alternative cooling with advantages of simplicity and compact. Using a natural refrigerant, a vortex tube enclosure cooling is environmentally benign. In this paper, the performance of a vortex tube enclosure cooling, VTEC, is investigated experimentally. The VTEC system comprises of the vortex tube cooling, an enclosure with a volume space of 0.045 m3, an air compressor, a compressed air storage tank and a compressed air line. The VTEC system is tested for its efficiency and cooling potential in the laboratory. An operating condition is controlled by a pressure regulator for an inlet air pressure of 3 bars, for energy saving, and a cold flow rate is adjusted by a needle valve near the hot exit of a vortex tube for the cold fraction between 0 and 1. Accordingly, the analysis of experimental data shows the maximum isentropic efficiency of the vortex tube enclosure cooling is 0.37 at the cold mass fraction of 0.45. Air temperature in the enclosure is about 13°C in average.